Question

Apple reports that the average app download from its App Store earns the developer 17.5 cents (source: Forbes.com). A group of specialty app developers claims that the average for their apps is lower. In a sample of 100 of their apps, the group found that the average earnings per download was 16.2 cents.
a. Using 17.5 cents as your null hypothesis, calculate the p value for the sample result. Assume the population standard deviation is 5.4 cents.
b. Can the group use this sample result to make the case that the average earnings for their apps is less than 17.5 cents, if the significance level is set at .05? At .01? Explain your answers.